The present invention relates to viscous fluid heaters that have a rotor, a heating chamber and a radiator chamber. More particularly, the present invention relates to a viscous fluid heater that has a multi-part housing.
Much attention has recently been focused on engine-driven viscous fluid heaters as auxiliary heat sources for vehicles. Japanese Unexamined Utility Model Publication No. 4-11716 discloses a viscous fluid heater that has a heating chamber and a cylindrical radiator chamber. The radiator chamber is defined about the heating chamber and constitutes a part of a coolant circulation passage. The housing of the heater consists of two parts combined with each other. More specifically the housing consists of a casing having an opening and a cover that closes the opening of the casing. The casing has a double cylinder structure including a cylindrical inner wall and a cylindrical outer wall with one end closed by a bottom wall. The inner wall defines the heating chamber therein and the outer wall is formed about the inner wall. A plurality of radiator fins protrude from the outer surface of the inner wall into the radiator chamber. The radiator chamber is provided with an inlet port, through which circulating water enters the chamber, and an outlet port, through which the water is discharged to an external heating circuit.
A drive shaft is rotatably supported in the casing by a bearing. The drive shaft has a plurality of disk-shaped inner plates, which are secured to the drive shaft and accommodated in the heating chamber. The inner plates constitute a rotor, which integrally rotates with the drive shaft. A plurality of annular outer plates are formed on the inner surface of the inner wall of the casing. Each outer plate faces, or is aligned with, one of the inner plates of the rotor at a predetermined distance from the corresponding inner plate. Rotation of the drive shaft rotates the inner plates, or the rotor, relative to the outer plates in the casing inner wall. This causes the rotor to shear the viscous fluid and produces friction between the viscous fluid and the inner and outer plates. The viscous fluid is heated accordingly. Heat exchange takes place between the heated viscous fluid and the circulating water in the radiator chamber. This heats the circulating water and warms the passenger compartment as the water flows into the heating circuit.
In the above described prior art heater, the radiator chamber is defined about the heating chamber. If the heating chamber and the radiator chamber are relatively long in the axial direction, a guiding member must be provided in the radiator chamber for guiding the flow of circulating water along a desired course. However, forming the guiding member in the radiator chamber is difficult because the radiator chamber has a relatively narrow annular clearance between the inner wall and the outer wall of the casing and the inner wall and the outer wall are formed only on the casing. Further, forming fins in the radiation chamber for improving the heat exchange efficiency of the radiator chamber is difficult. Without the guiding member and the fins, circulating water entering the radiator chamber through the inlet port is not evenly distributed in the radiator chamber but directly flows from the inlet port to the outlet port and is discharged from the outlet port. This degrades the heat exchange efficiency of the radiator chamber.